(1) Field of the Invention
The invention relates to power savings in a unified memory environment. More specifically, the invention relates to unobtrusively capturing display data and storing it in a display buffer for refreshing the static display.
(2) Related Art
It is relatively common in prior art embedded systems to employ a unified memory subsystem. The main memory has a portion allocated as a frame buffer for the system display. The frame buffer holds one frame of display data. Accordingly, the host processor and display controller share the memory, and the display controller must steal bus bandwidth from the host processor in order to interleave its fetches from the memory to refresh the display. Moreover, when the main memory would be otherwise powered down, it must be kept active in order to service the display controller. This can represent a power drain an order of magnitude greater than if the main memory could power down in such circumstances.
Some prior art systems have employed a frame buffer which is separate from the main memory. However, providing an additional one to two megabytes, or even 128 kilobytes, of memory significantly increases the cost of such embedded systems. For this reason, embedded systems have continued to use the unified memory system, and the deficiencies discussed above have gone largely unaddressed.
In view of the foregoing, it would be desirable to be able to reduce both power consumption and bus bandwidth drain resulting from unified memory subsystems' handling of display data. It would further be desirable to address these issues without requiring hardware modifications in either the display controller or the host processor.